Molecular Crowding Alters the Interactions of Polymyxin Lipopeptides within the Periplasm of E. coli: Insights from Molecular Dynamics.

The cell envelope of Gram-negative bacteria is a crowded tripartite architecture that separates the cell interior from the external environment. Two membranes encapsulate the aqueous periplasm, which contains the cell wall. Little is known about the mechanisms via which antimicrobial peptides move through the periplasm from the outer membrane to their site of action, the inner membrane. We utilize all-atom molecular dynamics to study two antimicrobial peptides, polymyxins B1 and E, within models of the E. coli periplasm crowded to different extents. In a simple chemical environment, both PMB1 and PME bind irreversibly to the cell wall. The presence of specific macromolecules leads to competition with the polymyxins for cell wall interaction sites, resulting in polymyxin dissociation from the cell wall. Chemical complexity also impacts interactions between polymyxins and Braun's lipoprotein; thus, the interaction modes of lipoprotein antibiotics within the periplasm are dependent upon the nature of the other species present.

Computational microbiology of bacteria: Advancements in molecular dynamics simulations.

Microbiology is traditionally considered within the context of wet laboratory methodologies. Computational techniques have a great potential to contribute to microbiology. Here, we describe our loose definition of "computational microbiology" and provide a short survey focused on molecular dynamics simulations of bacterial systems that fall within this definition. It is our contention that increased compositional complexity and realistic levels of molecular crowding within simulated systems are key for bridging the divide between experimental and computational microbiology.

Electric-Field-Driven Translocation of ssDNA through Hydrophobic Nanopores.

The accurate sequencing of DNA using nanopores requires control over the speed of DNA translocation through the pores and also of the DNA conformation. Our studies show that ssDNA translocates through hourglass-shaped pores with hydrophobic constriction regions when an electric field is applied. The constriction provides a barrier to translocation and thereby slows down DNA movement through the pore compared with pores without the constriction. We show that ssDNA moves through these hydrophobic pores in an extended conformation and therefore does not form undesirable secondary structures that may affect the accuracy of partial current blockages for DNA sequencing.